1. Field of the Invention:
The present invention relates to a support device.
2. Description of the Related Art
Various kinds of thin films are formed on semiconductor wafers (which will be hereinafter referred to as wafers) in the process of manufacturing semiconductor devices. The forming of these films is carried out by locating a wafer boat on which many wafers are mounted in a reaction furnace or the like. 100 or 150 pieces of the wafers, for example, are mounted on the wafer boat at certain intervals. These wafers are transferred from a wafer cassette to the wafer boat. The wafer cassette is used as transporting means for wafers in a semiconductor element manufacturing process. The shape of the wafer boat is made suitable for a thin film forming device such as a reaction furnace.
The boat is taken out of the reaction furnace after the thin films are formed on the wafers in the furnace and the wafers on which the thin films have been formed are then transferred from the boat to their cassette, which is carried to a next process. There are two types of reaction furnaces. One of them is a horizontal type provided with a horizontal central axis. The other is a vertical type provided with a vertical central axis. These processes are automated.
The boat is supported on a support device and reciprocated between a wafers-transferring position and a boat-delivering position. The wafers-transferring position is that where the wafers are transferred from their cassette to the boat or from the boat to their cassette while the boat-delivering position denotes that position which is on an elevator which serves to carry the boat into or out of the reaction furnace, for example.
The reason why the boat is reciprocated while being supported on the support device is that the boat must be correctly positioned at boat-carrying, wafers-transferring and boat-delivering times.
FIG. 1 shows an arrangement of the conventional boat support device. Numeral 1 represents a boat made of quartz glass. When it is made of quartz glass, boat 1 has adequate heat-resistance. A plurality of grooves having a certain interval between adjacent ones are formed on both sides of boat 1 along the longitudinal direction thereof. Wafers 2 are fitted into these grooves at both their sides.
Boat 1 is mounted on boat supports 5 which form boat carrying system 3. Boat 1 is held between support members 6 which form boat support device 7 in such a way that support members 6 are pressed from outside against both ends of boat 1. Boat 1 is released from support members 6 when support members 6 separate from both ends of boat 1. Boat supports 5 are erected on movable plate 4 which is mounted on boat carrying system 3. Boat carrying system 3 reciprocates on rails 8 between the wafers-transferring and boat-delivering positions. While boat carrying system 3 is moving, boat 1 is supported on boat supports 5 and held between support members 6.
Boat 1 is positioned on boat carrying system 3 by controlling those cylinders (not shown) for lifting boat supports 5 and reciprocating support members 6.
However, all boats 1 are not necessarily the same in their shape, because of manufacturing errors. In other words, every boat supported and carried on the boat support device differs a little from the others in shape. Even when each of the cylinders is driven by such strokes as needed to correctly position boat 1 on boat carrying system 3, therefore, it sometimes happens that support members 6 cannot contact boat 1 or that they contact boat 1 too strongly. When support members 6 are left not contacted with boat 1, boat 1 cannot be positioned correctly and when they contact boat 1 too strongly, it may be broken.
When boat 1 cannot be positioned correctly, it becomes difficult to automatically transfer plural wafers 2 into their grooves respectively from their cassette to boat 1. As a result, it becomes difficult to automate the process of manufacturing semiconductor devices. Further, the throughput in the process of manufacturing semiconductor devices is thus made low.